Sir, - Denys la Petit invented the BC/AD system in 532 AD, 700 years before the introduction of the zero to the Roman numbering system. For 2000 to be the first year in the third millennium, there would have been needed a year zero between 1 BC and 1 AD. Therefore 2001 is the first year in the third, or second if you count the 1 AD to 1000 AD as the zeroth, millennium. - Yours, etc.,
Rocklands,
Castlebar,
Co Mayo.